The present invention relates to transducer operating circuitry and, more particularly, to novel circuitry for obtaining output information from a force/presssure sensor of the magnetoelastic type.
Several forms of force/pressure transducers are known which utilize magnetoelastic materials. One sensor for measuring a force acting along the axis of a stack of magnetoelastic rings, and causing a variation in the magnetic flux density saturation magnitude of the ring stack hysteresis loop thereof responsive to the magnitude of the axial force, is described and claimed in co-pending application Ser. No. 546,227, filed on even date herewith, assigned to the assignee of the present application and incorporated herein by reference in its entirety.
Some magnetoelastic sensors are of the type having a single electrical coil which is excited by a periodically-changing voltage waveform of constant magnitude, provided from a low-impedance source, and from which a force-measuring output is obtained by monitoring the single coil current. Other magnetoelastic sensors have a pair of separate coils, with a constant current excitation being applied to the first coil and the sensor response being measured by the magnitude of an output voltage produced across the second coil. However, in energizing, or driving, the core of a magnetoelastic sensing device, the core (or the material of the stacked rings in the aforementioned application) is typically driven into the magnetic saturation region. The driving coil current required to energize the core into the saturation region may be as much as fifty times greater than the current required to drive the magnetically-unsaturated core. Thus, whether the driving excitation voltage is a waveform of sine or square waveshape, the exciting coil current will often reach large fractions of an ampere, especially since it is highly desirable to utilize an excitation coil having a relatively few number of turns, especially for a magnetoelastic sensor core having short magnetic length. Since it is undesirable, for economic reasons, to increase the number of exciting coil turns, it is highly desirable to provide circuitry which not only allows the peak current to be controlled to relatively low levels and still allows the use of an exciting coil of relatively few turns, but also one which provides the required output to determine the change in magnetic flux density saturation level, and thus the magnitude of the force acting upon the sensor, in as simple a manner as possible.